1. Field of the Art
This invention relates to a video signal processing system to be used for processing video signals from a solid state image sensor device mounted on an electronic endoscope.
2. Prior Art
Electronic endoscopes have a solid image sensor device like a CCD incorporated into a tip end portion of an insert body to be inserted into an intracorporeal or intracavitary portion which needs examination, thereby picking up the image of the intracavitary portion of interest and displaying the image in color on a monitor screen. Because of the darkness of the intracavitary portion to be examined or diagnosed, it is necessary for an electronic endoscope to be equipped with an illumination means. For this purpose, the endoscope is connected to a light source and is internally provided with a light guide to transmit illuminating light from the light source to the tip end of the insert portion, illuminating an intracavitary portion of interest through a window provided at the distal end of the insert body.
In this manner, under illumination with light from the light source, the image of an intracavitary portion of interest is formed on the solid image sensor device by way of storage of signal charges in the respective picture elements which constitute the solid image sensor device, while reading out the signal charges to a signal processor. The solid image sensor device which is employed in an image pickup system of this sort is normally of a single element type for the purpose of minimizing the diameter of the insert body of the endoscope, and is generally driven by a sequential field system to obtain three field signals of red (R), green (G) and blue (B), which are synthesized into color video signals for display on a monitor screen.
The insert body of the endoscope, which is designed for insertion into narrow intracavitary portions, is desired to be as small as possible in diameter to lessen patient's pains and to improve its operationability at the time of insertion. However, since the insert body is densely packed with various component parts, the reduction of its diameter is naturally limited by the necessity for securing spaces for the component parts to be built in the insert portion. This applies especially to electronic endoscopes which need to allot a relatively broad space for a solid-state image sensor device, which is mounted at the fore end of the insert body along with other component parts of the image pickup system. The solid-state image sensor is usually provided with a wiring pattern and is mounted on a circuit board together with other components parts. It follows that the outer diameter of the highly packed tip end portion determines the thickness of the insert body as a whole, and minimization of the component parts of the image pickup system is extremely important to the reduction of the diameter of the entire insert body.